Tulipalin copolymers

ABSTRACT

Copolymers are disclosed comprising structural units derived from α-methylene-γ-butyrolactone, styrene, methyl methacrylate and acrylonitrile. The copolymers may be used as protective layers in multilayer articles that include UV sensitive substrate materials. The multilayer articles may also include a silicone hardcoat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.11/289,928, filed Nov. 30, 2005, which is incorporated herein byreference.

BACKGROUND

The invention relates generally to copolymers ofα-methylene-γ-butyrolactone with methyl methacrylate, styrene andacrylonitrile.

Polymers made from tulipalin, or α-methylene-γ-butyrolactone (MBL), havebeen known for more than 50 years (U.S. Pat. No. 2,624,723).

MBL is called tulipalin because it is present in relatively highconcentration in white tulips. The homopolymer is a brittle glassymaterial with a glass transition temperature (T_(g)) of 195° C.(Macromolecules 12, 546 (1979)). The monomer can be viewed as a cyclicanalogue of methyl methacrylate, and its reactivity in free radicalpolymerizations is comparable or even higher than methyl methacrylate(Akkapeddi, et al., Journal of Polymer Science: Polymer ChemistryEdition, v 20, 2819, (1982) and Polymer, vol. 20, 1215, (1979)). Theincrease in free radical reactivity presumably comes from the ringstrain of the molecule.

MBL readily copolymerizes with styrene and (meth)acrylate monomers, andcopolymers with (meth)acrylate esters, acrylonitrile and styrene havebeen reported (Journal of Polymer Science: Polymer Chemistry Edition, v20, 2819 (1982)). JP 9033736 discloses clear, heat-resistant resinscomposed of copolymers of MBL with (meth)acrylate monomers. U.S. Pat.No. 5,880,235 discloses MBL copolymers for producing cast glass andthermal dimensionally stable molding materials. U.S. Pat. No. 6,642,346discloses compositions that include MBL copolymers for automotive clearcoats and clear coat finishes. The patent teaches that introduction ofan exomethylene lactone or lactam imparts enhanced mar and scratchresistance to the finishes (col. 1, lines 63-65). U.S. Pat. No.6,723,790 discloses blends of MBL copolymers with other polymers. U.S.Pat. No. 6,841,627 discloses MBL graft copolymers and blends of thecopolymers with thermoplastic resins in order to obtain good opticalproperties and heat and weathering resistance. US 2003/0130414 describescompositions of MBL copolymers filled with alumina trihydrate fordecorative sheets and articles The compositions possess thermalresistance, hardness, scratch and mar resistance, antimicrobialproperties, lower coefficient of thermal expansion, high refractiveindex and high transparency. None of the references mention copolymersof MBL with styrene and methyl methacrylate (MMA) that have high Tg,weatherability and solvent resistance.

BRIEF DESCRIPTION

It has been unexpectedly discovered that the copolymers of MBL withstyrene and methyl methacrylate and of MBL with styrene, methylmethacrylate, and acrylonitrile have excellent weathering and vastlyimproved solvent resistance. T_(g) is much higher than the correspondingpolymers made with styrene and acrylonitrile (SAN) alone or styrene,acrylonitrile, and methyl methacrylate (MMA-SAN). A highly weatherablemultilayer article may be constructed therefrom.

Accordingly, in some embodiments, the present invention relates tocopolymers that comprise structural units derived fromα-methylene-γ-butyrolactone, styrene, methyl methacrylate andacrylonitrile. The copolymers have glass transition temperatures rangingfrom about 110° C. to about 175° C.

DRAWINGS

FIG. 1 is a graph showing weatherability of MBL copolymers in comparisonwith a styrene-acrylonitrile copolymer or a copolymer of styrene,acrylonitrile and methyl methacrylate.

DETAILED DESCRIPTION

In one aspect, the present invention relates to copolymers comprisingstructural units derived from α-methylene-γ-butyrolactone, styrene andmethyl methacrylate and to copolymers comprising structural unitsderived from α-methylene-γ-butyrolactone, styrene, methyl methacrylateand acrylonitrile. The copolymers typically have glass transitiontemperatures ranging from about 110° C. to about 175° C., particularlyfrom about 120° C. to about 150° C. In the MBL copolymers, the amount ofstructural units derived from α-methylene-γ-butyrolactone ranges fromabout 10% by weight to about 75% by weight, particularly from about 20%by weight to about 50% by weight, and more particularly from about 20%by weight to about 35% by weight. The amount of structural units derivedfrom styrene ranges from about 20% by weight to about 80% by weight,particularly about 20% by weight to about 50% by weight, and moreparticularly from about 25% by weight to about 40% by weight. The amountof structural units derived from methyl methacrylate ranges from about5% by weight to about 50% by weight, particularly from about 10% byweight to about 45% by weight, and more particularly from about 15% byweight to about 45% by weight. For copolymers containing structuralunits derived from acrylonitrile, the amount of such units ranges from5% by weight to about 40% by weight, and particularly from about 5% byweight to about 35% by weight. For all copolymers where amounts areexpressed as % by weight, the amount is based on total copolymer weight.Incorporation of MBL in an MMA-SAN polymer typically improves weatheringwhile simultaneously increasing Tg and improving chemical resistance,without imparting a yellow color upon melt processing.

Any of the known methods for polymerizing styrene and/or (meth)acrylatemonomers may be used to prepare the α-MBL copolymers. However, bulk andsolution polymerization processes, using solvents such asγ-butyrolactone, toluene, NMP, DMF and DMSO, are particularly suitable.

In other embodiments, the present invention relates to multilayerarticles comprising a protective layer disposed on a substrate. Theprotective layer includes a copolymer of α-methylene-γ-butyrolactonewith methyl methacrylate, styrene and/or acrylonitrile, and particularlyMBL copolymers as described above. The protective layer is typicallydisposed directly on the substrate, but in some cases, it may bedesirable to laminate the protective layer to the substrate by use of anadhesive or primer layer.

The protective layer may include additives such as fillers (clay, talc,etc.), reinforcing agents (glass fibers), impact modifiers,plasticizers, flow promoters, lubricants and other processing aids,stabilizers, antioxidants, antistatic agents, colorants, mold releaseagents, flame retardants, antioxidants, hindered amine lightstabilizers, and/or UV absorbing agents (UVA). Suitable UVAs includehydroxybenzophenones, hydroxyphenyl benzotriazoles, hydroxyphenyltriazines, cyanoacrylates, oxanilides, benzoxazinones; and particulateinorganic materials such as titanium oxide, cerium oxide, and zincoxide, having a particle size less than about 100 nanometers. Other UVAsknown in the art and disclosed in standard reference works such as“Plastics Additives Handbook”, 5th edition, edited by H. Zweifel, HanserPublishers, may also be used. Mixtures of UVAs may be particularlyeffective, especially mixtures of the abovementioned agents. In aparticular embodiment, the UVA is2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxy-phenol, sold by CIBA® asTINUVIN® 1577.

The amount of UVA for use in the protective layer ranges from about0.0005 wt. % to about 10 wt. %, particularly from about 0.001 wt. % toabout 10 wt. %, and more particularly from about 0.1 wt. % to about 5wt. %, based on the total weight of polymer in the protective layer. Thethickness of the protective layer in multilayer articles typicallyranges from about 2μ to about 2,500μ, preferably from about 10μ to about500μ and most preferably from about 50μ to about 250μ.

Substrates for use in the multilayer articles in various embodiments ofthe present invention are materials that are sensitive to UV radiation,i.e., they undergo some undesirable change upon exposure to UVradiation. The undesirable change is typically a change in color, butchemical and mechanical properties of the substrate may be affected aswell. The UV sensitive materials include thermoplastic and thermosetpolymers and copolymers and blends thereof. Suitable thermoplasticpolymers include polycarbonates, particularly aromatic polycarbonates,polyacetals, polyarylates, polyarylene ethers, including polyphenyleneethers, polyarylene sulfides, including polyphenylene sulfides,polyimides, including polyamideimides, polyetherimides,polyetherketones, including polyaryletherketones, polyetheretherketones,polyetherketoneketones, polyamides, polyesters, including liquidcrystalline polyesters, polyetheresters, polyetheramides,polyesteramides, and polyestercarbonates, aliphatic olefin andfunctionalized olefin polymers, including polyethylene, polypropylene,thermoplastic polyolefin (TPO), ethylene-propylene copolymer, polyvinylchloride, poly(vinyl chloride-co-vinylidene chloride), polyvinylfluoride, polyvinylidene fluoride, polyvinyl acetate, polyvinyl alcohol,polyvinyl butyral, polyacrylonitrile, (meth)acrylate polymers andcopolymers including polymethyl methacrylate (PMMA), and polymers andcopolymers vinylaromatic monomers includingacrylonitrile-butadiene-styrene copolymer (ABS) andacrylonitrile-styrene (ASA). In particular, the substrate may be one ormore homo- or co-polycarbonate, or a polycarbonate blend, or a blend ofpolycarbonate with other polymers, for example, blends of polycarbonateswith polyesters, ABS copolymers or ASA copolymers. Other thermoplasticpolymers may be present therein, but the above-described polymers orblends typically constitute the major proportion thereof.

Suitable polycarbonates include homo- and copolycarbonates comprisingstructural units of the formula

wherein each A¹ and A² is a monocyclic divalent aryl radical and Z is abridging radical in which one or two carbon atoms separate A¹ and A². Inparticular, A¹ and A² may be unsubstituted phenylene or substitutedderivatives thereof and the bridging radical Z may be methylene,cyclohexylidene or isopropylidene. More particularly, the polycarbonatesmay be bisphenol A polycarbonates. The polycarbonate may also be acopolyestercarbonate. Such polymers contain, in addition to thecarbonate units, ester units containing -A¹-Z-A²- moieties linked toaromatic dicarboxylate groups such as isophthalate and/or terephthalate.Suitable polyesters include poly(alkylene dicarboxylates), especiallypoly(ethylene terephthalate) (PET), poly(1,4-butylene terephthalate)(PBT), poly(trimethylene terephthalate) (PTT), poly(ethylenenaphthalate) (PEN), poly(butylene naphthalate) (PBN), poly(cyclohexanedimethanol terephthalate), poly(cyclohexanedimethanol-co-ethyleneterephthalate) (PETG), andpoly(1,4-cyclohexanedimethyl-1,4-cyclohexanedicarboxylate) (PCCD).

Suitable polyarylates include structural units derived from aromaticdihydroxy compounds and aromatic dicarboxylic acid compounds,particularly from terephthalate and/or isophthalate structural units incombination with bisphenol A and/or resorcinol. Suitable polyetherimidesare described in U.S. Pat. Nos. 3,803,085 and 3,905,942.

Blends of any of the foregoing polymers may also be employed. Theseinclude blends of thermoset polymers with thermoplastic polymers such aspolyphenylene ether, polyphenylene sulfide, polysulfone, polyetherimideor polyester. The thermoplastic polymer is typically combined withthermoset monomer mixture before curing. Also included are blends ofcellulosic materials and thermoset and/or thermoplastic polymers.

The substrate composed of polymeric materials may also incorporatefillers such as silicates, zeolites, titanium dioxide, stone powder,glass fibers or spheres, carbon fibers, carbon black, graphite, calciumcarbonate, talc, mica, lithopone, zinc oxide, zirconium silicate, ironoxides, diatomaceous earth, calcium carbonate, magnesium oxide, chromicoxide, zirconium oxide, aluminum oxide, crushed quartz, calcined clay,talc, kaolin, asbestos, cellulose, wood flour, cork, cotton andsynthetic textile fibers, especially reinforcing fillers such as glassfibers and carbon fibers, as well as colorants such as metal flakes,glass flakes and beads, ceramic particles, other polymer particles, dyesand pigments which may be organic, inorganic or organometallic.

The multilayer articles may be prepared by a variety of known processessuch as coating from a solvent, film lamination, profile extrusion,sheet extrusion, coextrusion, extrusion blow molding and thermoforming,and injection molding. For example, the protective layer and substratemay be coextruded to form a multilayer article.

In some embodiments, the multilayer articles may additionally include asilicone hardcoat disposed on the protective layer. In this respect, MBLcopolymers may be used as primers for a silicone hardcoat. The MBLcopolymers for use with silicone hardcoats include structural unitsderived from other vinyl monomers in addition to those from MBL.Suitable vinyl monomers include (meth)acrylic acid and derivativesthereof, such as methyl methacrylate, ethyl acrylate, butyl acrylate,hydroxyethyl methacrylate, acrylonitrile, butyl methacrylate, isobutylmethacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearylmethacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butylacrylate, -2-ethylhexyl acrylate, lauryl acrylate, hydroxyethylacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, acrylamideor methacrylamide, dimethylaminoethylacrylate and dimethylaminoethylmethacrylate, glycidyl acrylate and glycidyl methacrylate, and aromaticvinyl compounds, such as styrene, vinyl toluene, α-methyl styrene andt-butyl styrene. In particular, copolymers of MBL with methylmethacrylate, styrene, and/or acrylonitrile, including those describedabove, may be used.

There is no limitation with respect to the type of silicone hardcoatsthat may be used, other than that they adhere to the protectivelayer/primer. Therefore, coatings prepared from basic, neutral or acidiccolloidal silica may be used. Examples of the silicone hardcoats thatmay be employed when the MBL copolymers are employed as protectivelayers/primers include those prepared by hydrolyzing an aqueousdispersion of colloidal silica and a trialkoxysilane or mixtures oftrialkoxysilanes having the formula RSi(OR)₃, wherein each R isindependently an alkyl group having 1 to 3 carbon atoms or a substitutedor unsubstituted aromatic radical; preferably, a methyl group. Thehardcoat may include conventional additives such as compatibleultraviolet light absorbing agents, and polysiloxane polyethercopolymers. Other additives including thickening agents, pigments, anddyes may also be included for their conventionally employed purposes. Adescription of the preparation of suitable silicone hardcoats may befound in U.S. Pat. No. 4,373,061.

DEFINITIONS

In the context of the present invention, alkyl is intended to includelinear, branched, or cyclic hydrocarbon structures and combinationsthereof, including lower alkyl and higher alkyl. Preferred alkyl groupsare those of C₂₀ or below. Lower alkyl refers to alkyl groups of from 1to 6 carbon atoms, preferably from 1 to 4 carbon atoms, and includesmethyl, ethyl, n-propyl, isopropyl, and n-, s- and t-butyl. Higher alkylrefers to alkyl groups having seven or more carbon atoms, preferably7-20 carbon atoms, and includes n-, s- and t-heptyl, octyl, and dodecyl.Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groupsof from 3 to 8 carbon atoms. Examples of cycloalkyl groups includecyclopropyl, cyclobutyl, cyclopentyl, and norbornyl

Aryl and heteroaryl mean a 5- or 6-membered aromatic or heteroaromaticring containing 0-3 heteroatoms selected from nitrogen, oxygen orsulfur; a bicyclic 9- or 10-membered aromatic or heteroaromatic ringsystem containing 0-3 heteroatoms selected from nitrogen, oxygen orsulfur; or a tricyclic 13- or 14-membered aromatic or heteroaromaticring system containing 0-3 heteroatoms selected from nitrogen, oxygen orsulfur. The aromatic 6-to 14-membered carbocyclic rings include, forexample, benzene, naphthalene, indane, tetralin, and fluorene; and the5- to 10-membered aromatic heterocyclic rings include, e.g. imidazole,pyridine, indole, thiophene, benzopyranone, thiazole, furan,benzimidazole, quinoline, isoquinoline, quinoxaline, pyrimidine,pyrazine, tetrazole and pyrazole.

Arylalkyl means an alkyl residue attached to an aryl ring. Examples arebenzyl and phenethyl. Heteroarylalkyl means an alkyl residue attached toa heteroaryl ring. Examples include pyridinylmethyl andpyrimidinylethyl. Alkylaryl means an aryl residue having one or morealkyl groups attached thereto. Examples are tolyl and mesityl.

Alkoxy or alkoxyl refers to groups of from 1 to 8 carbon atoms of astraight, branched, cyclic configuration and combinations thereofattached to the parent structure through an oxygen. Examples includemethoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, and cyclohexyloxy.Lower alkoxy refers to groups containing one to four carbons.

Acyl refers to groups of from 1 to 8 carbon atoms of a straight,branched, cyclic configuration, saturated, unsaturated and aromatic andcombinations thereof, attached to the parent structure through acarbonyl functionality. One or more carbons in the acyl residue may bereplaced by nitrogen, oxygen or sulfur as long as the point ofattachment to the parent remains at the carbonyl. Examples includeacetyl, benzoyl, propionyl, isobutyryl, t-butoxy-carbonyl, andbenzyloxycarbonyl. Lower-acyl refers to groups containing one to fourcarbons.

Heterocycle means a cycloalkyl or aryl residue in which one to three ofthe carbons is replaced by a heteroatom such as oxygen, nitrogen orsulfur. Examples of heterocycles that fall within the scope of theinvention include pyrrolidine, pyrazole, pyrrole, indole, quinoline,isoquinoline, tetrahydroisoquinoline, benzofuran, benzodioxan,benzodioxole (commonly referred to as methylenedioxyphenyl, whenoccurring as a substituent), tetrazole, morpholine, thiazole, pyridine,pyridazine, pyrimidine, thiophene, furan, oxazole, oxazoline, isoxazole,dioxane, and tetrahydrofuran, triazole, benzotriazole, and triazine.

Substituted refers to structural units, including, but not limited to,alkyl, alkylaryl, aryl, arylalkyl, and heteroaryl, wherein up to three Hatoms of the residue are replaced with lower alkyl, substituted alkyl,aryl, substituted aryl, haloalkyl, alkoxy, carbonyl, carboxy,carboxalkoxy, carboxamido, acyloxy, amidino, nitro, halo, hydroxy,OCH(COOH)₂, cyano, primary amino, secondary amino, acylamino, alkylthio,sulfoxide, sulfone, phenyl, benzyl, phenoxy, benzyloxy, heteroaryl, orheteroaryloxy; each of said phenyl, benzyl, phenoxy, benzyloxy,heteroaryl, and heteroaryloxy is optionally substituted with 1-3substituents selected from lower alkyl, alkenyl, alkynyl, halogen,hydroxy, haloalkyl, alkoxy, cyano, phenyl, benzyl, benzyloxy,carboxamido, heteroaryl, heteroaryloxy, nitro or —NRR (wherein R isindependently H, lower alkyl or cycloalkyl, and —RR may be fused to forma cyclic ring with nitrogen).

Haloalkyl refers to an alkyl residue, wherein one or more H atoms arereplaced by halogen atoms; the term haloalkyl includes perhaloalkyl.Examples of haloalkyl groups that fall within the scope of the inventioninclude CH₂F, CHF₂, and CF₃.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner.

EXAMPLES Example 1 Copolymer Synthesis

Materials: α-Methylene-γ-butyrolactone was obtained from TCI, and methylmethacrylate, styrene, acrylonitrile all from Aldrich. All were purifiedfrom inhibitors using a basic alumina column right before use.

General polymerization procedure: A vacuum flask was charged with therequired amount of styrene, acrylonitrile, α-methylene-γ-butyrolactone,methyl methacrylate according to the target composition along withγ-butyrolactone as the solvent. AIBN was added as a radical initiator.Chain transfer agent can be added if desired. The concentration remainedbelow 50%, preferable 30% to avoid a reaction exotherm. The flask wasdegassed twice through a freeze-thaw cycle, with a nitrogen purge whenthawing. The heating oil bath temperature were kept at 65-70° C. for 4hours and then cooled down to room temperature. The polymer sample wasprecipitated into methanol twice and dried in a low temperature vacuumoven overnight. The polymer compositions were determined by quantitativeC₁₃ analysis.

Poly(styrene-co-acrylonitrile-co-methyl-methacrylate-co-α-methylene-γ-butyrolactone)were made in different ratios, with Mw ranging from 30 to 220 kDaltons.Compositions and molecular weights are shown in Table 1.

Molecular weight and polydispersity was determined relative topolystyrene standards on a Perkin Elmer Series 200 GPC equipped with aPolymer Laboratories size exclusion column (PLgel 5 μm MIXED-C, 300×7.5mm kept at 40° C.) using chloroform with 3.6% v/v isopropanol as themobile phase.

Tg was measured on a Perkin-Elmer DSC-7 with Pyris software. The typicalDSC sample size was 5˜10 mg and the DSC heating and cooling rates were20° C./min. Results are shown in Table 1. Tg of polymers with about20-30 mol % of α-methylene-γ-butyro-lactone was increased about 20-30%over compositions without -α-methylene-γ-butyro-lactone.

TGA Samples (3.5 to 7.0 mg) were tested in air using a Perkin Elmer TGA7 under temperature scanning with a heating rates at 10° C./minute. TheTGA analysis also showed that the copolymers were thermally stable up toat least 350° C.

TABLE 1 Compositions determined by NMR (Mass %) Product MW Sample #Styrene Acrylonitrile MMA Tulipalin Mw (K) PDI Tg, ° C.  7 34.18 0.0022.90 42.92 36.79 2.66 134.32  8 22.93 0.00 11.88 65.19 68.67 1.76160.03  9 21.71 0.00 6.22 72.07 55.17 1.88 173.39 11 23.96 0.00 23.0452.99 48.91 1.81 141.36 12 41.43 0.00 9.00 49.57 62.91 1.89 141.35 1425.97 9.99 13.09 50.95 78.60 1.80 146.35 17 34.06 7.49 5.95 52.49 76.191.04 138.03 19 47.26 6.02 9.29 37.43 112.00 2.47 131.90 20 49.38 7.606.33 36.69 121.00 2.41 135.40 22 49.64 9.77 9.76 30.82 98.70 2.88 131.2023 46.89 11.65 25.30 16.16 209.06 2.74 110 24 44.73 9.69 13.98 31.60141.64 3.11 133 26 79.59 0.00 0.00 20.41 137.11 1.25 124 27 48.98 0.0051.02 0.00 122.91 1.72 107 29 37.51 0.00 31.69 30.80 176.65 1.90 128 3142.17 0.00 26.37 31.46 76.49 1.92 130 32 26.66 0.00 34.96 38.38 175.842.01 135 33 34.40 7.92 29.45 28.22 227.42 1.96 126 34 48.35 4.38 0.7246.55 217.66 2.22 134 35 34.48 9.96 18.92 36.63 207.77 1.65 133 36 25.944.96 43.65 25.45 170.52 1.87 126 37 22.66 13.04 43.25 21.05 229.21 2.21118 38 27.56 0.00 40.79 31.66 148.28 2.90 127 39 35.84 10.37 28.15 25.6465.49 2.09 123 40 32.27 21.02 24.43 22.28 156.27 1.69 121 41 32.97 20.9923.04 23.00 146.09 1.85 138 42 31.78 20.16 23.06 25.00 52.85 1.85 130 4337.22 27.66 21.77 13.35 178.91 1.90 114 44 38.62 22.67 9.28 29.43 46.591.75 130.28 45 29.02 27.44 19.63 23.91 95.36 1.79 122.12 MMASAN 39.5015.00 45.50 0.00 145.00 2.79 94

Example 2 Weatherability Determination

Polymer powder samples were compression molded into films about 100microns thick, using Teflon coated aluminum foil as shim, a temperatureof about 160° C., and a pressure of 4000 psi in a Carver press. Thefilms were mounted on an aluminum frame and exposed in an Atlas Ci4000xenon arc Weatherometer. The xenon arc lamp had a CIRA (IR-reflectingquartz) inner filter and a soda lime glass outer filter to best matchsunlight. The samples were continuously irradiated (except for the sprayperiod) at an irradiance of 0.75 W/m²/nm at 340 nm. The black paneltemperature was 55° C. and the air temperature was 35° C. at a relativehumidity of 30%. The samples received 30 minutes of water spray once perweek.

Color measurements were made using a GretagMacbeth ColorEye 7000Aspectrometer in transmission mode. Color is reported as Yellow Indexaccording to ASTM D-1925. Results are shown in FIG. 1. All of the MBLcopolymers yellowed less than commercial SAN, or MMASAN.

Example 3 Solvent Resistance

The films were tested for resistance to strong bases and organicsolvents in comparison with SAN and MMASAN. MBL copolymer films wereprepared using the procedure shown in Example 2. The film was placed ina crystallization dish and a drop (25 μL) of testing chemical wasdelivered onto the film surface by dispensing pipette. The dish withsample was placed in a oven at 65° C. for 1 hour. Pass and failobservation was made regarding whether there was visible damage to thefilm. Results are shown in Table 2. The MBL copolymers demonstratedimproved chemical resistance.

TABLE 2 Solvent Resistance Sample # 10% NaOH Toluene 22 Pass Pass 29Pass Pass 33 Pass Pass 34 Pass Pass 35 Pass Pass 36 Pass Pass 37 PassPass 38 Pass Pass 40 Pass Pass 41 Pass Pass 43 Pass Pass 44 Pass Pass 45Pass Pass MMASAN Pass Fail SAN Pass Fail

Example 4 Multilayer Article

Preparation: For MMASAN 530, PMMA, SAN 581, and MBL (#33, #38, and #41)samples, a solution was made of 2.0 g of the caplayer polymer and 0.02 gTINUVIN® 1577 UV absorber (product of Ciba Specialty Chemicals) in 9 mLof chloroform. Compositions are displayed in Table 3.

TABLE 3 Compositions of Caplayer Polymers Composition by NMR, mass %molecular wt Mw/Mn Tg # Styrene Acrylonitrile MMA Tulipalin kilodaltonsPDI (° C.) MMASAN 530 39.5 15 45.5 0 145 2.79 94 PMMA (Elvacite ® 2041)100 ~95 SAN 581 75 25 ~100 33 34.4 7.92 29.45 28.22 227.42 1.96 126 3827.56 0 40.79 31.66 148.28 2.9 127 45 29.02 27.44 19.63 23.91 95.36 1.79122

MMASAN and SAN are Products of GE Advanced Materials Elvacite 2041 is aProduct of Lucite International

The solution was poured onto a glass plate, drawn using a 10 mil doctorblade, and the solvent was allowed to evaporate. The film was floatedfrom the glass using water and further dried for 2 hours at 65° C. in aforced air oven. The final films were approximately 40 microns thick.Portions of the films were laminated onto 2½″×2½″×⅛″ plaques of Lexan®140 polycarbonate resin containing 2% titanium dioxide pigment.Lamination was done in a heated press at 165° C. using contact pressurefor 3½ minutes followed by 4000 psi pressure for 1 minute, and 6000 psipressure for ½ minute. The caplayers were firmly adhered to thepolycarbonate surface. The sample with no caplayer was an unlaminatedLexan polycarbonate plaque.

Example 5 Toluene Resistance

A drop of toluene was placed on the surface of the sample at roomtemperature for one or two minutes then wiped off using a cotton swab.The surface was visually evaluated for damage and judged as either none,very slight, slight, severe, or very severe. Results are shown in Table4. The results show that the tulipalin-containing samples have good toexcellent resistance toward toluene while copolymers of styrene,acrylonitrile, and methyl methacrylate have very poor resistance.

TABLE 4 Toluene resistance and weathering data Toluene Composition ofResistance Yellowing caplayer 1 min 2 min ΔYI at 2785 kJ MMASAN 530severe NA 9.1 PMMA v. slight slight 2.6 SAN 581 severe NA 31.4 33 v.slight slight 11.6 38 v. slight slight 9.0 45 none none 5.2 none (PCcontrol) v. severe NA 20.4

Example 6 Accelerated Weathering of Multilayer Articles

Samples were exposed in an Atlas Ci35a xenon arc Weatherometer using theconditions shown in Table 5. Samples were removed after an exposureperiod of 2785 kJ/m²/nm measured at 340 nm. This amount of exposure isequivalent to approximately one year in Miami Fla. The color shift wasmeasured on a Macbeth Coloreye 7000A spectrometer as the change inYellowness Index (ΔYI) as defined by ASTM D1925. The results are shownin Table 4. They show that laminates made from the tulipalin-containingcopolymers have smaller color shifts than the unlaminated polycarbonate,SAN laminate, and either better than or comparable to the MMASANcopolymer.

TABLE 5 Settings for weathering exposure Setting Value Irradiance 0.77W/m²/nm at 340 nm Cycle: light 160 minutes dark/dry 5 minutes dark/spray15 minutes Black panel temp 70° C. Dry bulb temp 45° C. Relativehumidity 50% Inner filter Type S borosilicate Outer filter Type Sborosilicate

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A copolymer comprising structural units derived fromα-methylene-γ-butyrolactone, styrene, methyl methacrylate andacrylonitrile, wherein the copolymer has a glass transition temperatureranging from about 110° C. to about 175° C.
 2. The copolymer accordingto claim 1, having a glass transition temperature ranging from about120° C. to about 150° C.
 3. The copolymer according to claim 1, whereinthe amount of structural units derived from α-methylene-γ-butyrolactoneranges from about 10% by weight to about 75% by weight.
 4. The copolymeraccording to claim 1, wherein the amount of structural units derivedfrom α-methylene-γ-butyrolactone ranges from about 20% by weight toabout 50% by weight, based on total copolymer weight.
 5. The copolymeraccording to claim 1, wherein the amount of structural units derivedfrom styrene ranges from about 20% by weight to about 80% by weight,based on total copolymer weight.
 6. The copolymer according to claim 1,wherein the amount of structural units derived from styrene ranges fromabout 20% by weight to about 50% by weight, based on total copolymerweight.
 7. The copolymer according to claim 1, wherein the amount ofstructural units derived from styrene ranges from about 25% by weight toabout 40% by weight, based on total copolymer weight.
 8. The copolymeraccording to claim 1, wherein the amount of structural units derivedfrom methyl methacrylate ranges from about 5% by weight to about 50% byweight, based on total copolymer weight.
 9. The copolymer according toclaim 1, wherein the amount of structural units derived from methylmethacrylate ranges from about 10% by weight to about 45% by weight,based on total copolymer weight.
 10. The copolymer according to claim 1,wherein the amount of structural units derived from methyl methacrylateranges from about 15% by weight to about 45% by weight, based on totalcopolymer weight.
 11. The copolymer according to claim 1, wherein theamount of structural units derived from acrylonitrile ranges from about5% by weight to about 40% by weight, based on total copolymer weight.12. The copolymer according to claim 1, wherein the amount of structuralunits derived from acrylonitrile ranges from about 5% by weight to about35% by weight, based on total copolymer weight.
 13. The copolymeraccording to claim 1, wherein the amount of structural units derivedfrom α-methylene-γ-butyrolactone ranges from about 10% by weight toabout 75% by weight, the amount of structural units derived from styreneranges from about 20% by weight to about 80% by weight, the amount ofstructural units derived from methyl methacrylate ranges from about 5%by weight to about 50% by weight, and the amount of structural unitsderived from acrylonitrile ranges from about 5% by weight to about 40%by weight, based on total copolymer weight.
 14. The copolymer accordingto claim 1, wherein the amount of structural units derived fromα-methylene-γ-butyrolactone ranges from about 20% by weight to about 50%by weight, the amount of structural units derived from styrene rangesfrom about 20% by weight to about 50% by weight, the amount ofstructural units derived from methyl methacrylate ranges from about 10%by weight to about 45% by weight, and the amount of structural unitsderived from acrylonitrile ranges from about 5% by weight to about 35%by weight, based on total copolymer weight.
 15. A copolymer comprisingstructural units derived from 25-35% by weightα-methylene-γ-butyrolactone, 25-40% by weight styrene, 15-45% by weightmethyl methacrylate and 5-35% by weight acrylonitrile, based on totalcopolymer weight, wherein the copolymer has a glass transitiontemperature ranging from about 110° C. to about 175° C.